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Abstract:

The invention relates to a novel assembly for coating substrates.

Claims:

1. An arrangement for completely or partially coating support bodies
(121) with liquid coating medium (124), wherein the support bodies (121)
each have a cylinder axis, two end faces, a circumferential surface and
an axial length L and are traversed from the first end face to the second
end face by a multiplicity of channels, and the support body (121) is
coated with a desired quantity of the coating medium (124) by aligning
the cylinder axis thereof vertically and introducing the coating medium
(124) into the channels through at least one of the end faces of the
support body, wherein the support body (121) is arranged on a coating
device (122), the liquid-carrying part of which is connected by a valve
(125) to a riser tube (127), wherein the valve (125) ensures the same
pressure conditions and hence substantially the same rise in the liquid
in the riser tube (127) as in the support body, the riser tube (127) thus
allowing the filling level (FH) of the coating medium (124) in the
support body (121) to be monitored.

2. The arrangement as claimed in claim 1, wherein the filling level (FH)
is less than the axial length L of the support body.

3. The arrangement as claimed in claim 1, wherein monitoring of the
filling level (FH) of the coating medium (124) in the support body (121)
is effected by means of at least one sensor (126) on the riser tube
(127).

4. The arrangement as claimed in claim 3, wherein the sensors are
selected from the group comprising conductivity sensors, ultrasound
sensors, photoelectric barriers and combinations thereof.

5. A method for completely or partially coating support bodies (121) with
liquid coating medium (124), wherein the support bodies (121) each have a
cylinder axis (A), two end faces (131, 132), a circumferential surface
(130) and an axial length L and are traversed from the first end face
(131) to the second end face (132) by a multiplicity of channels (133),
wherein the support body (121) is arranged on a coating device (122), the
liquid-carrying part of which is connected by a valve (125) to a riser
tube (127), wherein the valve (125) is set to ensure the same pressure
conditions and hence substantially the same rise in the liquid in the
riser tube (127) as in the support body (121), the riser tube (127) thus
allowing the filling level of the coating medium (124) in the support
body (121) to be monitored, the support body (121) is coated with a
desired quantity of the coating medium (124) by aligning the cylinder
axis (A) thereof vertically and introducing the coating medium (124) into
the channels (133) through at least one of the end faces (131, 132) of
the support body; the rise in the filling level (FH) is monitored at the
riser tube (127) and, when a desired filling level (FH) has been
achieved, a further rise in the liquid is prevented.

6. The method as claimed in claim 5, wherein the further rise in the
filling level (FH) is prevented by removing the coating medium (124) from
the support body (121).

7. The method as claimed in claim 6, wherein removal is accomplished by
pumping, extraction by suction or blowing out.

8. The method as claimed in claim 5, wherein the coating operation is
repeated.

9. The method as claimed in claim 8, wherein the support body (121) is
turned through 180.degree. before the coating operation is repeated, and
is then coated, with the result that coating starts from the opposite end
face of the support body (121).

10. The method as claimed in claim 8, wherein the coating medium (124)
when the coating operation is repeated is the same as or different from
the coating medium in a preceding coating operation.

11. The method as claimed in claim 5, wherein the support body (121) is
subjected to at least one heat treatment in a subsequent step.

12. A method for producing exhaust systems containing coated support
bodies (121), wherein at least one support body (121) is coated by a
method of claim 5 and at least one support body (121) coated in this way
is connected to the exhaust system.

13. The method as claimed in claim 12, wherein the exhaust system is an
exhaust system of a motor vehicle.

14. A method for producing a coated support body for cleaning exhaust
gases comprising utilizing the arrangement of claim 1 to coat a supplied
support body.

Description:

[0001] Various problems arise during the coating of ceramic or metallic
honeycomb bodies/filters, also referred to below as substrates, with
liquid coating media.

[0002] One possibility for coating substrates is to bring the openings on
one side thereof into contact with the coating medium made available and
to draw the liquid coating medium through the channels of the substrate
by applying a vacuum to the opposite side of the substrate. If the
intention is to coat the channels over only part of the length thereof,
it is disadvantageous that different channels are coated over different
lengths due to the inevitable flow profile which arises.

[0003] If the coating medium is forced into the channels by pressure
against the force of gravity, there is then a need to check when the
liquid emerges at the top in the case of complete coating of the
channels. In the case of coating over part of the length of the channels,
the height of the liquid column of coating medium within the channels is
determined by sensors. A method of this kind is described in
EP-A1-1273344, for example.

[0004] However, this method does not work if the substrate is composed of
conductive or semiconductive materials, such as metals or silicon
carbide.

[0005] It was the object of the invention to provide a simple device for
coating support bodies which allows the filling level of coating medium
within the support body to be tracked easily, irrespective of the
material thereof. The object is achieved by virtue of the fact that the
liquid-carrying part of the coating device (122) is connected by a valve
(125) to a riser tube (127), wherein the valve (125) ensures the same
pressure conditions and hence substantially the same rise in the liquid
in the riser tube (127) as in the support body, the riser tube (127) thus
allowing the filling level of the coating medium (124) in the support
body (121) to be monitored.

BRIEF DESCRIPTION OF THE INVENTION

[0006] Specific embodiments of the invention relate inter alia to: [0007]
1. An arrangement for completely or partially coating support bodies
(121) with liquid coating medium (124), wherein the support bodies (121)
each have a cylinder axis, two end faces, a circumferential surface and
an axial length L and are traversed from the first end face to the second
end face by a multiplicity of channels, and the support body (121) is
coated with a desired quantity of the coating medium (124) by aligning
the cylinder axis thereof vertically and introducing the coating medium
(124) into the channels through at least one of the end faces of the
support body, characterized [0008] in that the support body (121) is
arranged on a coating device (122), the liquid-carrying part of which is
connected by a valve (125) to a riser tube (127), wherein the valve (125)
ensures the same pressure conditions and hence substantially the same
rise in the liquid in the riser tube (127) as in the support body, the
riser tube (127) thus allowing the filling level of the coating medium
(124) in the support body (121) to be monitored. [0009] 2. The
arrangement according to point 1, wherein the filling level is less than
the axial length L of the support body. [0010] 3. The arrangement
according to point 1 or 2, wherein monitoring of the filling level of the
coating medium (124) in the support body (121) is effected by means of at
least one sensor (126) on the riser tube (127). [0011] 4. The arrangement
according to point 3, wherein the sensors are selected from the group
comprising conductivity sensors, ultrasound sensors, photoelectric
barriers and combinations thereof. [0012] 5. A method for completely or
partially coating support bodies (121) with liquid coating medium (124),
wherein the support bodies (121) each have a cylinder axis, two end
faces, a circumferential surface and an axial length L and are traversed
from the first end face to the second end face by a multiplicity of
channels, wherein the support body (121) is arranged on a coating device
(122), the liquid-carrying part of which is connected by a valve (125) to
a riser tube (127), [0013] characterized in that [0014] the valve (125)
is set to ensure the same pressure conditions and hence substantially the
same rise in the liquid in the riser tube (127) as in the support body,
the riser tube (127) thus allowing the filling level of the coating
medium (124) in the support body (121) to be monitored, [0015] the
support body (121) is coated with a desired quantity of the coating
medium (124) by aligning the cylinder axis thereof vertically and
introducing the coating medium (124) into the channels through at least
one of the end faces of the support body; [0016] the rise in the filling
level is monitored at the riser tube (127) and, when a desired filling
level has been achieved, a further rise in the liquid is prevented.
[0017] 6. The method according to point 5, wherein the further rise in
the filling level is prevented by removing the coating medium (124) from
the support body (121). [0018] 7. The method according to point 6,
wherein removal is accomplished by pumping, extraction by suction or
blowing out. [0019] 8. The method according to point 5, wherein the
coating operation is repeated. [0020] 9. The method according to point 8,
wherein the support body (121) is turned through 180° before the
coating operation is repeated, and is then coated, with the result that
coating starts from the opposite end face of the support body (121).
[0021] 10. The method according to point 8 or 9, wherein the coating
medium (124) when the coating operation is repeated is the same as or
different from the coating medium in a preceding coating operation.
[0022] 11. The method according to one of points 5 to 10, wherein the
support body (121) is subjected to at least one heat treatment in a
subsequent step. [0023] 12. The method according to point 11, wherein the
support body (121) is dried before the heat treatment. [0024] 13. The
method according to one of points 5 to 11, wherein the support body is
wetted before being arranged on the coating device (122). [0025] 14. A
method for producing exhaust systems containing coated support bodies
(121), wherein at least one support body (121) is coated by a method of
claims 5 to 12 and at least one support body (121) coated in this way is
connected to the exhaust system. [0026] 15. The method according to point
14, wherein the exhaust system is an exhaust system of a motor vehicle.
[0027] 16. The use of a device according to one of points 1 to 4 for
producing coated support bodies for cleaning exhaust gases.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention relates to an arrangement for completely or
partially coating support bodies (121) with liquid coating medium (124).

[0029] Illustrative embodiments are described in FIGS. 1 to 11, in which:

[0030] FIG. 1 shows a coating system consisting of a coating device (122),
a tank (144) for the coating medium (124) and a vacuum reservoir (141),
wherein a feed line (120), an outlet line (140) and a return line (142)
containing a recirculation pump (143) for coating medium (124) are
provided.

[0033] FIG. 4 shows another operating option for the coating device (122)
shown in FIGS. 1 to 3, and

[0034] FIG. 5 to FIG. 11 show examples of the method sequences according
to the invention in accordance with claims 5 to 11 in the form of block
diagrams.

[0035] The support body (121), often also referred to as a substrate, is
generally a hollow substrate which is composed of metals or ceramics and
has at least one inner channel, generally a multiplicity of inner
channels (133). The support bodies are generally substantially
cylindrical support bodies, which each have a cylinder axis (A), two end
faces (131, 132), a circumferential surface (130) and an axial length L
and are traversed from the first end face to the second end face by a
multiplicity of channels. Such support bodies are often also referred to
as honeycomb bodies. In particular, the support bodies can be throughflow
honeycomb bodies, or alternatively wall flow filters, which can have a
high cell density (number of inner channels per area of cross section) of
about 10 cm-2 to 250 cm-2. The support body can be composed of
cordierite, mullite, aluminum titanate, silicon carbide or a metal such
as steel or stainless steel, for example. The support body is
advantageously a monolithic, cylindrically shaped catalyst support body
and is traversed by a multiplicity of flow channels (133) parallel to the
cylinder axis (A) for the exhaust gases from internal combustion engines.
Such monolithic catalyst support bodies are used on a large scale for the
production of automotive exhaust gas catalysts. The cross-sectional shape
of the catalyst support bodies depends on the installation requirements
on the motor vehicle. Catalyst bodies with a round cross section, an
elliptical, an oval or a triangular cross section are widely used. The
flow channels generally have a square cross section and are arranged in a
narrowly spaced pattern over the entire cross section of the catalyst
bodies. The channel or cell density of the flow channels generally varies
between 10 and 250 cm-2, depending on the application. For exhaust
gas purification on motor cars, catalyst support bodies with cell
densities of about 62 cm-2 are still frequently used nowadays.

[0036] If the support body (121) is composed of silicon carbide or a metal
such as steel or stainless steel, detecting the filling level is more
difficult, and the present invention provides a new procedure for solving
this problem. However, this procedure can of course also be used to coat
support bodies made of cordierite, mullite or other materials.

[0037] The support bodies (121) each have a cylinder axis (A), two end
faces (131, 132), a circumferential surface (130) and an axial length L
and are traversed from the first end face to the second end face by a
multiplicity of channels (133). The support body (121) is coated with a
desired quantity of the coating medium (124) by aligning the cylinder
axis (A) thereof vertically and introducing the coating medium (124)
through at least one of the end faces of the support body (121). For this
purpose, the support body (121) is arranged on the coating device (122),
advantageously in a liquid-tight manner, it being possible to achieve
this by means of at least one seal (146). The seal can be hollow and can
be filled with gas or liquid as it is mounted on or inserted into the
coating device, and can form a leaktight closure. The leaktightness of
the joint can be monitored by means of a pressure or flow sensor.

[0038] The coating medium (124) is then introduced into the support body
(121) against the force of gravity, as shown in FIGS. 1 to 3, it being
possible to achieve this by applying an excess pressure to the coating
medium (124), thus bringing about a rise in the filling level (FH) of
coating medium (124) in the support body (121). During this process, a
certain quantity of coating medium (124) is made available by the
delivery pump (135). When the liquid level approaches the first end face
(131) of the support body (121), a signal can be transmitted by the
sensors (123) to the central computer (150), which, depending on the
embodiment of the invention, can emit a cutoff signal for the delivery
pump (135) or actuate a valve in order to interrupt further inflow of
coating medium. A similar procedure can be achieved by using an excess
quantity controlled by a dosimeter (136) to provide the supply of coating
medium (124) (FIG. 3).

[0039] The coating medium (124) can also be introduced by applying a
vacuum to the top of the support body (121). For this purpose, the
coating medium (124) is drawn into the support body (121) by pumping or
applying a vacuum, by means of a suction fan (145) or a vacuum reservoir
for example, as shown in FIG. 4. For this purpose, it is of course
necessary for the same vacuum to be applied to the riser tube (127) as
well and, in one specific embodiment of the invention, a seal (147) is
provided between an extraction hood (148) and the support body (121).

[0040] The coating medium (124) is liquid and, for example, a suspension
or dispersion for coating exhaust gas filters for motor vehicles
("washcoat") which contains catalytically active components or precursors
thereof and inorganic oxides such as aluminum oxide, titanium dioxide,
zirconium oxide or a combination thereof, it being possible for the
oxides to be doped with silicon or lanthanum, for example. Oxides of
vanadium, chromium, manganese, iron, cobalt, copper, zinc, nickel or rare
earth metals such as lanthanum, cerium, praseodymium, neodymium,
promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium,
erbium, thulium, ytterbium or combinations thereof can be used as
catalytically active components. Noble metals such as platinum,
palladium, gold, rhodium, iridium, osmium, ruthenium and combinations
thereof can also be used as catalytically active components. These metals
can also be present as alloys with one another or with other metals or as
oxides. The metals can also be present as precursors, such as nitrates,
sulfites or organyls of said noble metals and mixtures thereof, and, in
particular, palladium nitrate, palladium sulfite, platinum nitrate,
platinum sulfite or Pt(NH3)4(NO3)2 can be used in the
liquid coating medium. By calcination at about 400° C. to about
700° C., the catalytically active component can then be obtained
from the precursor. To coat a support body for the production of
automotive exhaust gas catalysts, a suspension or dispersion of an
inorganic oxide can initially be used for coating, after which, in a
subsequent coating step, a suspension or dispersion which contains one or
more catalytically active components can be applied. However, it is also
possible for the liquid coating medium to contain both these components.
The liquid coating medium often has a solids content of between 35 and
52% and a viscosity of between 15 and 300 cps.

[0041] During coating in the arrangement of the invention, the support
body (121) is arranged on a coating device (122), the liquid-carrying
part of which is connected by a valve (125) to a riser tube (127),
wherein the valve (125) ensures the same pressure conditions and hence
substantially the same rise in the liquid in the riser tube (127) as in
the support body, the riser tube (127) thus allowing the filling level
(FH) of the coating medium (124) in the support body (121) to be
monitored. The invention is particularly advantageous if the filling
level (FH) is less than the axial length L of the support body (121).
Otherwise, it is also possible for the filling level to be detected as
the liquid emerges at the upper end face of the support body and for the
coating operation to be ended. The arrangement of the invention allows
the filling level (FH) of the coating medium (124) in the support body
(121) to be monitored by means of at least one sensor (126) on the riser
tube (127).

[0042] In one specific embodiment of the invention, additional sensors
(123) can be mounted on the coating device (122) in order to ensure a
sufficient filling level (FH) of coating medium (124) within the coating
device (122) for coating the support body (121). It is possible here to
provide sensors (126a, 126b, 126c, 126d) which allow the filling level
(128a, 128b) in the riser tube (127) and/or in the support body (121) to
be determined and to be compared with one another and with the
predetermined filling level (FH) by means of the central computer (150).
The central computer (150) can readjust the valve (125) by means of the
actuator (A1). In principle, any suitable sensors can be used for sensors
(123) and (126), these preferably being selected from the group
comprising conductivity sensors, ultrasound sensors, photoelectric
barriers, refractive index sensors, capacitive sensors and combinations
thereof. For detection of the filling level (FH) in the riser tube (127),
the sensor (126a), can be arranged laterally, as is the case, for
example, with a photoelectric barrier or a conductivity sensor, which
emits a signal to trigger the ending of the coating operation when the
liquid front is crossed. If changed levels are detected, the laterally
arranged sensor can be rearranged mechanically, i.e. shifted along the
riser tube (127), for example. If the sensor, that is to say, for
example, an ultrasound sensor (126b), which operates on the principle of
echo sounding, is arranged above the riser tube (127), the filling level
can be tracked by measurement in the course of the coating operation. In
this case, a change in the arrangement of the sensor when there is a
change in the desired filling level is not required.

[0043] With the device of the invention, a method for completely or
partially coating support bodies (121) with liquid coating medium (124)
is carried out, the support body or bodies (121) being arranged on a
coating device (122), the liquid-carrying part of which is connected by a
valve (125) to a riser tube (127). The valve (125) is set (FIG. 1), in
one specific embodiment of the invention to a fixed value, so that the
same pressure conditions and hence substantially the same rise in the
liquid in the riser tube (127) as in the support body (121) are ensured,
the riser tube (127) thus allowing the filling level of the coating
medium (124) in the support body (121) to be monitored.

[0044] For this purpose, it is possible, for example, for a support body
(121) of a type for which calibration of the valve (125) is to be carried
out to be arranged on the coating device (122). At the same time, the
filling level (FH) in the support body (121) is also checked in order to
enable the filling levels (128a and 128b) in the riser tube (127) and the
support body (121) to be compared or correlated with one another. For
this purpose, the support body (121) can, for example, be provided with a
sensor (126d) for determining the filling level (FH) and, in the case of
support bodies made of silicon carbide or metal, the sensor (126c) can be
arranged above the upper end face of the support body and detect the
emergence of the coating medium (124). Depending on whether the filling
level (FH) rises more quickly in the support body (121) or in the riser
tube (127), the valve (125) can then be adjusted accordingly in order to
adapt the rise in the filling level in the riser tube (127) to the rise
in the filling level (FH, 128b) in the support body (121). For this
purpose, a number of setting tests may be necessary in order to perform
appropriate adjustment of the valve (125). Depending on the properties of
the support body (121) and of the coating medium (124), it may be
necessary to replace the support body (121) with a new, uncoated support
body since, in the case of certain combinations of support bodies and
compositions of coating medium, the rise in the filling level within the
support body may be altered by previously applied coating medium (124)
which is already present. For a particular type of support body, such
adjustment of the valve (125) must be carried out for different
compositions of the coating medium (124). The data obtained (times,
filling levels, compositions and/or viscosities of the coating medium,
applied excess pressures or vacuums, types of support body etc.) are
entered in tables in a mutually correlated manner. It is particularly
advantageous here if, in addition, not only types of support body but
also the properties thereof which determine the pressure conditions
during coating are likewise entered, e.g. cell densities, lengths, cell
sizes, making it possible to perform a rough pre-adjustment of the valve
(125) during subsequent valve adjustments involving different coating
media and support bodies, on the basis of the known data and the
properties of the new types of support body and coating suspensions to be
used, and allowing precise adjustment to be performed more quickly. It is
particularly advantageous if valve adjustment is performed automatically,
e.g. under computer control. In this case, a readjustment is either
initiated by an operator or by the central computer (150), or is
triggered automatically on the basis of changes in the properties of the
coating medium (such as conductivity or viscosity) or a change in the
type of support body, it being possible for this to be detected
automatically by means of a barcode for example. The valve (125) is then
adjusted by means of an actuator (A1), e.g. a servo. The filling levels
of the support body (121) and the riser tube (127) are determined with
the aid of the sensors and those required to achieve predetermined
filling levels are compared by the central computer (150), in which case
the computer then performs the adjustment of the valve (125) and, if
required, of previously determined values entered in tables by means of
an actuator (A1) and, if appropriate, repeats the adjustment until a
predetermined accuracy is achieved. After the adjustment of the valve
(125), the support bodies (121) can be coated with a desired quantity of
the coating medium (124) by aligning the cylinder axis (A) of the support
body (121) vertically and introducing the coating medium (124) into the
channels (133) through at least one of the end faces (131, 132) of the
support body. As described above, this can be accomplished in various
ways, such as pumping, the application of an excess pressure or the
application of a vacuum. If a vacuum is applied, this must likewise be
applied to the riser tube. During the coating of an individual support
body (121), the rise in the filling level (FH) is monitored at the riser
tube (127) and, when a desired filling level has been achieved, a further
rise in the liquid is prevented. A further rise in the liquid is
prevented by stopping the inward-pumping operation or reducing the excess
pressure or vacuum in relation to ambient pressure. This generally brings
about removal of the coating medium (124) from the support body (121),
this being accomplished, in particular, by pumping, suction or blowing.
If, namely, as in EP-A1-941763 for example, the coating medium (124) is
brought about by applying a vacuum to the coating device (122), e.g. via
the feed line (120), the surrounding normal pressure causes a flow of gas
through the channels of the support body (121), which not only removes
the coating medium filling the channels but can also be used to remove
any excess quantity of coating medium (124) that may be adhering to the
side walls of the channels within the support body (121).

[0045] To remove the coating medium (124), a vacuum can be applied to the
lower end faces (131), via an outlet line (140) for example, e.g. by
opening an extraction valve (137) leading to an evacuated vacuum
reservoir (141) (FIG. 1). At the same time, air or some other gas which
is inert with respect to the coated support body and the coating
suspension, such as nitrogen, can be supplied from the upper end faces
(132) of the support body to the upper end faces without being
pressurized. Since the pressure in the vacuum reservoir falls, there is
therefore also a reduction in the flow rate of the gas in the channels of
the support bodies. A procedure of this kind is described in
EP-A1-941763, page 4, line 56 to page 5, line 36, for example, to which
reference is made.

[0046] However, the procedure can also be reversed and the vacuum applied
to the upper end faces and gas supplied to the lower end faces of the
support bodies. It is likewise also possible for this supply to be
changed or reversed one or more times, bringing about more uniform
coating of the channels in the support bodies according to U.S. Pat. No.
B 7,094,728.

[0047] Instead of applying a vacuum ("emptying or freeing the support
bodies by suction"), it is also possible to apply an excess pressure
("blowing out" the support bodies). For this purpose, air or some other
gas which is inert with respect to the coated support bodies and the
coating suspension, such as nitrogen, is supplied to the upper or lower
end face under pressure. During this process, the end faces which lie
opposite the end faces subjected to gas pressure must ensure that a
sufficient quantity of gas can flow off. For this purpose, a vacuum can
be applied, but this is not absolutely essential. However, a gas or
liquid pressure should not also be applied from the opposite sides to
ensure a gas flow rate sufficient to remove excess coating suspension
from the channels of the support bodies. In this case too, as in the
method according to U.S. Pat. No. B 7,094,728 outlined in brief above,
the excess pressure can be supplied alternately from the upper and lower
end faces.

[0048] The coating operation of the invention can also be repeated, either
to bring about complete coating of the support bodies by means of two
partial coating steps or, alternatively, to apply different coatings one
on top of the other or to different sections of the support body. These
procedures are known in principle in the prior art. Depending on the
procedure, the coating medium (124) used upon repetition of the coating
operation can therefore be the same as or different from the coating
medium in a preceding coating operation.

[0049] Before a repetition of the coating operation, the support body
(121) can advantageously be turned through 180° and then coated,
with the result that coating starts from the opposite end face (132) of
the support body (121) from the end face (131) from which coating started
in the preceding coating operation.

[0050] After removal of the coating medium (124), the support bodies (121)
are, if appropriate, dried and subjected to a heat treatment (calcined).
Before the heat treatment, the support bodies can be dried. This measure
is optional since the support bodies are dried in any case during the
subsequent heat treatment.

[0051] For drying, a flow of preheated air at a temperature of between 20
and 150° C. flowing at a rate of more than 4, preferably 7-10 m/s,
for 5 to 20 s can be passed through the channels (133) of the support
body (121), from below against the force of gravity for example, after
removal from the coating device. By means of this type of pre-drying
before heat treatment, clogging of the flow channels or narrowing of the
channels at the lower end of the support bodies, which is often observed
at very high rates of charge, can be avoided. This additional measure
makes it possible to charge the support body with a higher quantity of
coating than normal without the flow channels closing up or narrowing
during the drying and calcination process. The concentration of the
coating dispersion on the support body can thus be increased by this
measure.

[0052] The heat treatment is generally carried out at a temperature of
about 150° C. to about 800° C., in particular at about
200° C. to 700° C., advantageously at about 250° C.
to about 600° C. The time for heat treatment is about 1 to 5,
advantageously 2 to 3 hours at a heating rate of about 10° C./min
to about 50° C./min, in particular about 20° C./min to
about 40° C./min, advantageously about 35° C./min to about
45° C./min, the heating rates relating to the temperature of the
furnace. In the case of batchwise heat treatment, the heating rates can
be achieved by appropriate controlled heating of the furnace or, in a
continuous process, by controlling the feed rate of the support bodies
through a tunnel furnace, which is operated with a defined temperature
profile.

[0053] In one specific embodiment of the method of the invention, the
support body is wetted before being arranged on the coating device. In
the dry state, the support bodies have a considerable absorption capacity
for liquids. Particularly when coating highly cellular support bodies
with cell densities of 120 cm-2 and above, this can lead to
solidification of the coating medium and blockage of the flow channels
even during the filling process. It is therefore advantageous to wet the
support bodies before coating. This can be a matter of pre-impregnation
with an acid, a base or a salt solution. Pre-impregnation facilitates the
formation of the coating on the channel walls by the sol-gel method.
Contact between the coating dispersion and the pre-impregnated channel
walls shifts the pH of the dispersion, a suitable dispersion used as a
coating medium thereby being converted into a gel.

[0054] The present invention also relates to a method for producing
exhaust systems containing coated support bodies (121), wherein at least
one support body (121) is coated by the method of the invention and at
least one support body (121) coated in this way is connected to the
exhaust system, i.e. the coated support body is inserted or installed in
the exhaust system in such a way that the stream of exhaust gas flows
through the fully coated support body and the pollutant content of the
exhaust gases is reduced. The exhaust system is, in particular, an
exhaust system of a motor vehicle. The device of the invention can
therefore be used to produce coated support bodies for cleaning exhaust
gases.